1. Field of the Invention
The invention relates to a process and a contactless battery charging device. More particularly, the invention relates to devices using communication by modulation of a supply electromagnetic field and furthermore having a battery to operate outside the supply electromagnetic field.
2. Description of the Related Art
In the world of smart cards, or other similar small portable devices with integrated circuits, an external power supply has been used for a very long time. One of the main reasons is that it is not easy to integrate a battery into an object of small size. Thus, the communication protocols used require a power supply for the card, either by contact, for example the ISO 7816 protocol, or without contact, for example the ISO 14443 protocol.
In the ,world of contactless smart card readers, it is common to couple a peripheral card reader to a personal computer (PC). The PC/SC standard was defined by the PS/SC Workgroup in order to standardise data exchanges between PC and card. The PC/SC standard is most often used to exchange data between the host and contactless device. The PC/SC standard uses the communication protocol defined in ISO standard 14443-4, better known under the heading T=CL, intended for exchange of messages commonly called frames or “Blocks”, in which three types of blocks are distinguished:                I-Blocks: blocks enabling information exchange between a reader and contactless device.        R-Blocks: blocks enabling receipt of blocks previously sent between a reader and a contactless device to be acknowledged.        S-Blocks: blocks enabling synchronisation of the communication protocol between a reader and a contactless device.        
The PC/SC standard has the particular feature of implementing a detection mode that, when no “useful” data is transmitted between the reader and the contactless device (suspended communication), allows the reader to know if the contactless device is still present or has been removed from the reader, by regularly exchanging “non-useful” blocks with the device. The PC/SC standard proposes two types of blocks, sent by the reader, enabling detection of the presence of the contactless device:                R-Block(NAK): during receipt of this block the contactless device retransmits the last block of information sent.        Empty I-Block: during receipt of this block the contactless device replies with an information block that is also empty or contains an error status.        
Moreover, batteries even just a few hundred micrometers thick can be made to enable them to be integrated into the body of the card. In the case of rechargeable batteries, their use is currently limited to cards where the supply is made by contact in order to have a sufficient energy contribution.
However, recharging a battery through the electromagnetic communication field poses a few problems. The electromagnetic field serves to supply the card on the one hand and to communicate with the card on the other. This double use of the electromagnetic field only just enables supply of the chip in the smart card while modulating the field for communication. Over-consumption, which could be associated for example with recharging an internal battery in the smart card, would cause a disturbance in the electromagnetic field that could also induce communication errors between the card and the reader. In addition, data exchanges between the reader and the card being totally unpredictable, no time interval can be reserved by the card to carry out this recharging. Consequently, it is advisable to make preferential use of a more appropriate means of charging the battery.